I am in the process of supercharging my Expedition and have 33" BFG's with the stock 3:55 gears. With the supercharging I also wanted to get the correct gears under it. I do a little towing, but it is only a 19' boat which tows very easily. I was told that the 4:56 may be a little much since I tow. Some day I may even go up one size on the tires (even though I like the way it sits now). Any help or advise you guys can give me would really be appreciated. Oh, by the way my Expy is the A4WD model so I only want to do this one time since I have to get two sets of gears at the same time.

 

I run 4.10s on 31.5 inch street tires 285/60R18).

If you stick with 33s I think 4.10s are good, but a 4.56 isn't all that much shorter so it's borderline...I think I'd lean toward the 4.10s though, unless your trailer was really heavy.

With an upgrade to a 35 inch tire, I'd go with 4.56 for sure.

 

From what I understood was that the 4.56 would be too much gear for the towing I do. I was told that the correct gear ratio for my setup was right in between the 4.10 and the 4.56. My boat and trailer tow very well (it almost seems like they are not there with the current gears, until you go up hill which is a little struggle with the 3.55's). I just don't want to get the 4.10's and then have the "oops I could have had a V8" (4.56's) scenario. It's always nice to have a little room to grow because what I choose now will have to stay put. Any other opinions will definately be welcome and appreciated.

Thanks,
Mel

 

I spoke with tech support at;
http://www.fordracingparts.com
The gentleman I spoke with was very Knowledgeable concerning gear ratios and how to figure out the correct gearing for spacific setups on Fords. He took into account everything from the transmission I have to the diameter of my tires and how far they would roll in one revolution. His calculations came up with my tires being 33.4". I can't remember all the other numbers he was calculating but he definately seemed to know his stuff. With my set up, these tires and 4.56 gears my truck would be putting out 2200 rpm at 70 mph. He said that I could go with either 4.10's or 4.56's but if it were him he would definetly go with the 4.56 and possibly larger but recommended I go with the 4.56. Well I ordered my parts from Randy's Ring & Pinion. I'm getting the 4.56 Yukon gears and a Detroit True Track. They should be here Thursday and I pick up my truck Friday from the supercharger install. I hope I can get to sleep tonight. CAN'T WAIT. Oh yea, I will be having the gears installed by a professional shop. No need winging it now.

 

I was looking into getting new gears too and i have 33's as well. I wasnt sure if going to a 4.56 would hurt my fuel mileage too badly tho. I know the 4.10s will be good, but will i really feel the increase enough for it to be worth it? Which ones will i get better MPG with?

thanks in advance

 

The guy at Ford that I talked to told me that I may even see a slight increase in gas mileage because it will be taking less from the engine to get the truck moving. Of course, (his words) that all depends on how much you keep your foot out of the gas peddle. He did know the reality of that when I am getting supercharged and other performance mods along with these gears. Go to this site and call the tech support at the bottom of the page. Very enlightening!! http://www.fordracingparts.com/

 

I think that should call those guys because im not sure how much me not adding a supercharger will affect my situation. Im jealous by the way. I just want to get some ooooomf back and raise my mpg too.

 

It means that the added torque multiplication will be even more noticeable for you.

 

I think your gas mileage will defineately improve. I have a 1995 f150 5.8 5 speed with 3.55's. I towed my camper with it yesterday for the first time and I had to bury the throttle to get it going and maintian speed on the hills. Once it was rolling or I had an even flow of traffic it was no problem, but boy did it guzzle the gas. I also have a 2005 Chevy Avalanche with a 4.10. It won't outrun my F150 on the highway, but it pulls that heavy camper with a lot less effort. BTW I'm ordering 4.10's for the F150 this week.